This invention relates to imaging systems and particularly to such systems which employ arrays of receiving elements.
An object which is actively illuminated may be conceived of as a highly randomized phased array which radiates a far-field pattern expressible as a two-dimensional Fourier Transform of the excitation distribution currents induced by the incident or illumination field. In general, to accurately reconstruct the magnitude and phase of this source distribution, or more accurately an N .times. M sample function representative thereof, N .times. M sample points in the far field, are required and normally N .times. M receivers are needed. For example, at an operating frequency of 10.6 .mu.m, for 30 centimeter resolution of an object at 35,000 meters, a matrix of approximately 50 .times. 50, i.e. 2500, receiving element might be required. As the required resolution and/or imaging range increases, for the standard "full matrix" approach, the number of required receiving sites increases so rapidly as to be prohibitive from a cost viewpoint. For the above example, a 100 .times. 100 receiving matrix would provide only a modest increase in performance while requiring 10,000 receiving sites. Also, it is expected that employing convention array thinning techniques to replace an N .times. M array with N + M spatial samples would produce relatively poor quality imagery.